Viscous clutch fluid capture system

ABSTRACT

A viscous clutch (20; 120; 220) includes an input member (24; 126; 224), an output member (26; 124; 226), a working chamber (38; 138; 238), a reservoir (36; 136; 236; 504; 604; 704; 804; 904; 1004; 1104) to hold a supply of a shear fluid, an outlet (36-2; 182; 236-2; 512; 612; 712; 812; 912; 1012; 1112), a return bore (26-2; 124B; 226-2), an accumulator (72; 502; 602; 702; 802; 902; 1002; 1102), and a first wall (70-1; 170; 270; 506; 606; 706; 806; 906; 1006; 1106) having an arcuate segment (70-1A; 506B; 606B; 706B; 806B; 906B; 1006B; 1106B). The reservoir is connected to the working chamber by a fluid circuit, along which the outlet passes the shear fluid from the reservoir to the working chamber and the return bore returns the shear fluid pumped out of the working chamber to the accumulator. The accumulator is arranged in series with the reservoir in the fluid circuit. The first wall is positioned within the reservoir to separate a first portion from a second portion.

FIELD

The present invention relates to viscous clutches, and, moreparticularly, to a fluid capture system to reduce or prevent “morningsickness” in viscous clutches.

BACKGROUND

Viscous clutches are used in a wide variety of automotive fan driveapplications, among other uses. These clutches employ a relatively thickshear fluid or viscous fluid (typically silicone oil) for the selectivetransmission of torque between two rotating components. It is possibleto engage or disengage the clutch by selectively allowing the shearfluid into and out of a working area of the clutch located between inputand output members (e.g., between an input rotor and an output housing).A valve is used to control the flow of the shear fluid in the workingarea between the input and the output members. Recent clutch designshave been employed that allow the shear fluid to be stored in therotating input portion of the clutch while the clutch is disengaged, inorder to keep kinetic energy available to the shear fluid to allow rapidengagement of the clutch from the off condition. This also allows theclutch have a very low output speed (e.g., fan speed) while in the offposition. It has also become common for the clutch to be controlledelectrically. This has been done to increase the controllability of theclutch, and to also have the clutch capable of responding to multiplecooling needs in a vehicle. Some of the possible cooling needs arecoolant temperature, intake air temperature, air conditioning pressure,and oil temperature.

However, viscous clutches suffer from a problem commonly referred to as“morning sickness”. The problem of morning sickness arises because ofthe presence of openings or bores that fluidically connect the reservoirand the working chamber. When the clutch is “off”, such as when avehicle in which the clutch is installed sits unused overnight, theshear fluid can drain back from the reservoir into the working chamber.The drain-back problem is often dependent upon the rotational (orangular) orientation of the clutch when the clutch comes to rest, withgravity tending to induce relatively large volumes of drain back fluidinto the working chamber when an opening or bore is rotated so as to bein a lower part of the clutch where that fluid settles. When the vehicleis started, such as a “cold start” the next morning after non-useovernight, the migration or drain-back of the shear fluid into theworking chamber can cause significant engagement between the input andoutput members. For a fan clutch, this can cause relatively high speedfan engagement upon vehicle start-up, which can generate unwanted noiseand unwanted cooling effects. Even though the clutch will eventuallypump unwanted shear fluid out of the working area to disengage theoutput member, it would be more desirable to reduce or avoid any timeperiod of clutch engagement due to morning sickness fluid drain-back.

A variety of solutions have been proposed to address the problem of“morning sickness”. Many of those known designs utilize relativelycomplex structures that make clutch manufacturing and assembly moredifficult. Moreover, known morning sickness prevention mechanisms canundesirably increase a size of the clutch in the radial and/or axialdirection.

Therefore, it is desired to provide an alternative viscous clutch systemthat reduces “morning sickness”.

SUMMARY

A viscous clutch according to one aspect of the present inventionincludes an input member, an output member, a working chamber definedbetween the input member and the output member, a reservoir to hold asupply of a shear fluid, an outlet, a return bore, an accumulator toaccept the shear fluid from the return bore, and a first wall having anarcuate segment. The reservoir is fluidically connected to the workingchamber by a fluid circuit. The outlet is configured to pass the shearfluid from the reservoir to the working chamber along the fluid circuit,and the return bore is configured to return the shear fluid pumped outof the working chamber along the fluid circuit. The accumulator isarranged in series with the reservoir in the fluid circuit. The firstwall is positioned within the reservoir to separate a first portion ofthe reservoir from a second portion of the reservoir.

In another aspect, a method for use with a viscous clutch includespumping a shear fluid radially inward from a working chamber to anaccumulator, passing the shear fluid from the accumulator to a reservoirhaving a closed configuration, separating a first portion of thereservoir from a second portion of the reservoir with a first arcuatewall located within the reservoir, delivering the shear fluid from thereservoir to the working chamber, and bringing the viscous clutch torest in an idle condition. Portions of the shear fluid are retained inboth the accumulator and the first portion of the reservoir in the idlecondition to reduce drain back from the reservoir to the workingchamber.

In yet another aspect, a method for use with a viscous clutch includespumping a shear fluid radially inward from a working chamber to anaccumulator, passing the shear fluid from the accumulator to a reservoirhaving a closed configuration, moving all of the shear fluid from theaccumulator along a reservoir path having a tortuous shape thattraverses an angular range of at least 540° relative to an axis of theclutch, delivering the shear fluid from the reservoir to the workingchamber, and bringing the viscous clutch to rest in an idle condition.Portions of the shear fluid are retained in both the accumulator and anupstream portion of the reservoir path in the idle condition to reducedrain back from the reservoir to the working chamber.

The present summary is provided only by way of example, and notlimitation. Other aspects of the present invention will be appreciatedin view of the entirety of the present disclosure, including the entiretext, claims and accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an embodiment of a viscous clutchaccording to the present invention.

FIG. 2 is a perspective view of a portion of the clutch of FIG. 1.

FIG. 3 is a cross-sectional view of another embodiment of a viscousclutch according to the present invention, shown only above a centralaxis.

FIG. 4 is a cross-sectional view of another embodiment of a viscousclutch according to the present invention, shown only above a centralaxis.

FIGS. 5-11 are schematic views of different embodiments of a viscousfluid capture system for a viscous clutch according the presentinvention.

While the above-identified figures set forth embodiments of the presentinvention, other embodiments are also contemplated, as noted in thediscussion. In all cases, this disclosure presents the invention by wayof representation and not limitation. It should be understood thatnumerous other modifications and embodiments can be devised by thoseskilled in the art, which fall within the scope and spirit of theprinciples of the invention. The figures may not be drawn to scale, andapplications and embodiments of the present invention may includefeatures, steps and/or components not specifically shown in thedrawings.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

In general, the present invention relates to a viscous clutch having aninput member (e.g., a rotor disk), an output member (e.g., a housing), aworking chamber between the input and output members, and a reservoirfor holding a supply of a shear fluid (e.g., silicone oil). Engagementand disengagement of the clutch can control rotation of a componentcoupled to the output member, such as a fan. The clutch can beselectively engaged by moving shear fluid from the reservoir to theworking chamber, which creates a torque coupling between the input andoutput members at a given slip speed. The reservoir is designed to trapa quantity of shear fluid when the clutch is in an idle or “off” state,without a rotational input, to help reduce a phenomenon known as“morning sickness”, which typically occurs when the shear fluid canpassively drain back from the reservoir into the working chamber duringthe idle state. Numerous embodiments are disclosed for accomplishingmorning sickness reduction. In certain embodiments, at least one partialwall is provided within the reservoir to divide portions of thereservoir from each other and to separate and isolate fluid in one ormore portions of the reservoir from one or more other portions of thereservoir. The wall(s) can have an arcuate (e.g., circular arc-shape,spiral/helical, etc.) segment, as described further below, or havevarious other suitable shapes and configurations. The reservoir can beclosed, meaning that the reservoir can be essentially sealed except fortwo bores, forming an inlet and an outlet, respectively. In someembodiments, the wall(s) allow one or more portions of the reservoir tocapture (that is, accumulate and temporarily retain) at least a portionof the shear fluid, isolated from any inlet or outlet bores, to reduceor prevent shear fluid drain-back and other “morning sickness” effects.In other embodiments, the wall(s) create a tortuous path between inletand outlet bores; such a tortuous path can extend about an axis of theclutch through an angular range of 180° or more (such as 360° or more).The wall(s) can provide a fluid space with a varying cross-sectionalarea in some embodiments, such that shear fluid can be stored away frombores. An accumulator can be provided adjacent to and/or upstream of thereservoir in some embodiments, to limit “morning sickness” effects. Theaccumulator can be used in conjunction with any embodiment of thepartial wall(s) within the reservoir, or can be used alone (i.e.,without any wall within the reservoir). These features and benefits aredescribed merely by way of example and not limitation. Numerous otherfeatures and benefits of the present invention will be recognized bythose of ordinary skill in the art in view of the entirety of thepresent disclosure, including the accompanying figures.

The present application is based on and claims the benefit of U.S.provisional patent application Ser. No. 62/262,565, filed Dec. 3, 2015,and further claims priority to International patent application SerialNo. PCT/US2016/55258, filed Oct. 4, 2016, the contents of which are eachhereby incorporated by reference in their entireties.

FIG. 1 is a cross-sectional view of an embodiment of a viscous clutch 20that includes a shaft 22, a multi-part housing (or housing assembly) 24,a rotor 26, a hub 28, a mounting disk 30, a valve assembly 32 (onlypartly visible in FIG. 1), an electromagnet 34, a reservoir 36, and aworking chamber 38. Additional components are discussed below. Featuresof the viscous clutch 20 can be the same as or similar to thosedisclosed in International patent application Serial No.PCT/US2016/55258.

The shaft 22 in the illustrated embodiment is a “live” center shaft,meaning that the shaft 22 is rotatable and is located at a center of theclutch 20 defined by an axis of rotation A. The shaft 22 extends axiallythrough at least part of the housing 24, and is rotatably fixed to thehousing 24 at or near a front face of the housing 24. In the illustratedembodiment, the shaft 22 can act as a primary structural support for theentire clutch 20, which is to say that mass of the clutch 20 can besupported primarily (or entirely) by the shaft 22. The shaft 22 can beconnected to a torque input, such as a driveshaft of an engine (notshown), so that the shaft 22 accepts an input torque and acts as adriving or input member for the clutch 20.

The housing 24 includes a base 24-1 and a cover 24-2 secured to eachother in a rotationally fixed manner In the illustrated embodiment, oneend of the shaft 22 is affixed to a center sleeve (or hub) of the cover24-2, and the base 24-1 is indirectly supported on the shaft 22 by thecover 24-2. In this way, the base 24-1 has a cantilevered orsemi-cantilevered configuration. The housing 24 can be made of aluminumor another suitable material. Cooling fins 24-3 can be provided onexternal surfaces of the housing 24, on the base 24-1 and/or the cover24-2, to facilitate heat dissipation to ambient air. One or more seals40 can also be provided along the housing 24 (e.g., between the base24-1 and the hub 28) to help retain shear fluid within the clutch 20.Because the housing 24 is rotationally fixed to the shaft 22, thehousing 24 rotates whenever the shaft 22 rotates. When the shaft 22accepts torque input to the clutch 20, the housing 24 rotates at aninput speed as a function of a torque input to the shaft 22, with boththe housing 24 and the shaft 22 rotating whenever there is torque inputto the clutch 20. In that way, the cooling fins 24-3 can rotate with thehousing 24 at the input speed whenever input torque is provided to theclutch 20, which helps enhance heat dissipation as compared to havingfins on an output member that rotates only when the clutch is engaged.

The rotor 26 is positioned at least partially within the housing 24, andpreferably entirely within the housing 24, and can have a disk-likeshape with a central opening 26-1. The rotor 26 can be made of aluminumor another suitable material. When the shaft 22 and the housing 24 actas torque input members of the clutch 20, the rotor 26 (together withthe hub 28 and the mounting disk 30) acts as a torque output member. Inthe illustrated embodiment, the shaft 22 and/or a portion of the housing24 passes through the central opening 26-1 in the rotor 26, separated bya small radial gap, allowing transmission of torque from the shaft 22 tothe housing 24 along a torque transmission path.

The working chamber 38 is defined (and operatively positioned) betweenthe rotor 26 and the housing 24. The working chamber 38 can extend toboth sides of the rotor 26. As explained further below, selectiveintroduction of a shear fluid (e.g., silicone oil) to the workingchamber 38 can engage the clutch 20 by creating a viscous shear couplingto transmit torque between the housing 24 and rotor 26, with the degreeof torque transmission (and associated output slip speed) being variablea function of the volume of shear fluid present in the working chamber38. Concentric annular ribs, grooves and/or other suitable structurescan be provided on the rotor 26 and housing 24 to increase surface areaalong the working chamber 38 and promote a shear coupling when the shearfluid is present in the working chamber 38, as is known in the art. Therotor 26 can further include a fluid return bore 26-2 that extendsgenerally radially from the working chamber 38 to the reservoir 36, asexplained further below.

The hub 28 is a generally axially-extending, sleeve-like member that canserve multiple functions, including providing structural support forvarious clutch components, a torque transmission path, and part of amagnetic flux circuit. The rotor 26 is rotationally fixed to the hub 28,and the hub 28 is further rotationally fixed to the mounting disk 30,which can act as an output of the clutch 20. The hub 28 can be affixedto the rotor 26 at or near the central opening 26-1. Additionally, thehub 28 can be rotationally supported on the shaft 22 by a bearing set42. It should be noted that the particular configuration of the hub 28shown in the drawings and described above is provided merely by way ofexample, and not limitation. For instance, a portion of the hub 28 couldbe integrated with the rotor 26 or have a different (e.g., non-stepped)shape in further embodiments, and an additional bearing set canoptionally be provided proximate to the rotor 26. The hub 28 can be madeof a suitable magnetic flux-conducting material, such as a ferromagneticmaterial like steel, in order to serve as part of a flux circuit, asexplained further below.

The mounting disk 30 is rotationally fixed to the hub 28, which providesa rotational coupling (e.g., a fixed or direct rotational torquecoupling) between the rotor 26 and the mounting disk 30, enabling themounting disk 30 to co-rotate at the same speed as the rotor 26 (e.g.,at the output slip speed). An output device 44, such as a fan, can beconnected and rotationally fixed to the mounting disk 30. The mountingdisk 30 can be positioned at or near a rear face of the housing 24, andat least a portion of the mounting disk 30 extends outside the housing24. Such a configuration allows for a rear mount of the output device44, and, in an embodiment where the output device 44 is a fan, allowsthe fan to be positioned behind the clutch 20 (i.e., between the clutch20 and the location where the live shaft 22 is mounted).

The valve assembly 32 selectively controls flow of the shear fluidbetween the reservoir 36 and the working chamber 38. In the illustratedembodiment, the reservoir 36 is provided on or within the housing 24,and more particularly in the base 24-1 of the housing 24, and a plate36-1 of the reservoir 36 can be attached to and carried by the housing24 to form a boundary to help retain the shear fluid and to separate thereservoir 36 from other portions of the clutch 20. The plate 36-1 can belocated in an interior of the clutch 20, and can be arranged to face therotor 26. The shear fluid can be stored in the reservoir 36 when notneeded for engagement of the clutch 20. In the illustrated embodiment,the reservoir 36 is carried by the housing 24, such that the reservoir36 and shear fluid contained within both rotate with the housing 24. Inthis way, when the shaft 22 and the housing 24 act as an input to theclutch 20, the reservoir 36 rotates at input speed whenever there is atorque input to the clutch 20, which imparts kinetic energy to the shearfluid in the housing-carried reservoir 36 to facilitate relatively quickclutch engagement response times. Furthermore, because the reservoir 36is carried by the housing 24, which is an exterior component of theclutch 20, the reservoir 36 and the shear fluid contained therein arelocated in close physical proximity to the both ambient air and the fins24-3, which facilitates heat dissipation as compared to clutches havinga reservoir on or carried by interior clutch components (like therotor).

The clutch 20 can be electromagnetically controlled, meaning thatselective energization of the electromagnet 34 can control operation ofthe valve assembly 32, and in turn the degree of engagement between theinput and output members. Although not all of the subcomponents of thevalve assembly 32 are visible in FIG. 1, magnetic flux from theelectromagnet 34 can move (e.g., translate) an armature, which in turncan move (e.g., translate) a control rod, which in turn can move (e.g.,pivot) a valve element. The valve element can limit or prevent flow ofthe shear fluid out of the reservoir 36 when in a closed position. Insome embodiments, referred to as a “fail on” configuration, the valveelement can be mechanically biased to an open position by default, withenergization of the electromagnet 34 causing the valve element to moveto the closed position. In some embodiments, the configuration andoperation of the valve assembly 32 can be similar to that described incommonly-assigned PCT Patent Application Pub. No. WO2014/047430A1 orInternational patent application Ser. No. PCT/US2016/55258. However, itshould be noted that the particular configuration of the valve assembly32 disclosed herein is provided merely by way of example and notlimitation. Numerous other types of valve configurations can be utilizedin alternative embodiments, such as valves with pivoting or rotatingelements, as well as valves that selectively cover the fluid return bore26-2. Moreover, bimetal-controlled valve assemblies can be used in thefurther embodiments instead of an electromagnetically controlled valveassembly, as are well-known in the art.

Accumulators/chambers 70 and/or 72 can also be provided in the clutch20, as discussed further below.

FIG. 2 is a perspective view of a portion of the clutch 20, includingthe base 24-1 of the housing 24 and the reservoir 36, shown inisolation. As shown in FIG. 2, an outlet bore or port 36-2 is formedalong a boundary of the reservoir 36 to allow the shear fluid to leavethe reservoir 36 for delivery to the working chamber 38. In theillustrated embodiment, the outlet bore 36-2 is formed in the plate36-1, at a location radially inward from a radially outer perimeter ofthe plate 36-1, and allows the shear fluid to pass out of the reservoir36 in a substantially axial direction (i.e., parallel to the axis A ofthe clutch 20). The outlet bore 36-2 can be selectively covered anduncovered by the valve element of the valve assembly 32 (not shown inFIG. 2), which governs how much of the shear fluid can flow out of thereservoir 36 and to the working chamber 38 and thereby control the slipspeed of the clutch 20. It should be noted that in alternate embodimentsthe plate 36-1 can be integrally and monolithically formed with otherstructures forming all or part of the boundary of the reservoir 36. Inthe illustrated embodiment, the reservoir 36 is closed, such that theshear fluid can only enter or leave the reservoir 36 through twoopenings, the outlet bore 36-2 and an inlet bore (described below).

During operation of the clutch 20, the shear fluid can be continuallypumped from the working chamber 38 back to the reservoir 36 through thereturn bore 26-2. The return bore passes through the rotor 26 in theillustrated embodiment, but in alternative embodiments could be in thehousing 24 (e.g., in the cover 24-2). A dam or baffle can be positionedadjacent to the return bore 26-2 in the working chamber 38 to facilitatepumping the shear fluid back to the reservoir 36, in a manner well-knownin the art.

A fluid circuit is provided by the clutch 20. The shear fluid can movealong the fluid circuit during operation of the clutch 20. In brief, thefluid circuit can extend from the reservoir 36 to the working chamber 38via the outlet bore 36-2, then from the working chamber back to thereservoir 36 via the return bore 26-2. In the illustrated embodiment,the fluid circuit also passes through the accumulator 72, which isarranged in between the return bore 26-2 and the reservoir 36 (in flowseries). As already noted, flow of the shear fluid through the outletbore 36-2 can be selectively controlled by the valve assembly 32. In atleast some alternate embodiments, a reservoir path can be formed withinthe reservoir 36, to create a tortuous path traveled by at least some ofthe shear fluid held in the reservoir.

The present invention includes embodiments of features to help reduce orprevent so-called “morning sickness” when a clutch receives a rotationalinput after a period of inactivity (i.e., an idle period). “Morningsickness” relates to shear fluid draining back to the working chamberwhile idle (i.e., without any input torque), such that the clutchengages briefly before the shear fluid can be pumped back to thereservoir upon receipt of an input torque. It is desirable for theviscous clutch 20 to retain as much of the shear fluid as possible awayfrom the working chamber 38, such as in the reservoir 36, when theclutch 20 is not used for an extended period of time.

The reservoir 36 can be partitioned or otherwise divided into separateportions to facilitate capture and retention of the shear fluid duringidle conditions to reduce or prevent morning sickness effects, that is,drain-back of the shear fluid to the working chamber 38. To that end,the sub-chamber (or accumulator) 70 can be defined within the reservoir36 by a wall 70-1 having an arcuate segment 70-1A that extends over anangular range β with respect to the axis A of the clutch 20 betweenopposite ends 70-1B and 70-1C. In some embodiments, the angular range βcan be selected such that 180°≤β<360° (in alternative embodimentsdiscussed below, the angular range β of a wall within a reservoir can begreater than 360°). In some preferred embodiments, the angular range βis relatively large, such as greater than 270°. In the illustratedembodiment, the angular range β is approximately 315°.

A projection 70-1P can be provided at or near the end 70-1B of the wall70-1. The projection 70-1P can extend over a radial distance, and canconnect the arcuate segment 70-1A of the wall 70-1 to a boundary of thereservoir 36. In the illustrated embodiment, the projection 70-1Pextends radially inward from the arcuate segment 70-1A to a radiallyinner boundary of the reservoir 36, and creates a “dead end” of thesub-chamber (accumulator) 70 such that the shear fluid cannot pass theend 70-1B or otherwise move between inner and outer sides of the wall70-1 at or near the end 70-1B. In the illustrated embodiment, theprojection includes an internal hole or passageway, which is fluidicallyisolated from the reservoir 36 but provides a space for a control rod ofthe valve assembly 32 (not shown in FIG. 2) to pass through thereservoir 36 while maintaining the reservoir in a closed configuration.

The end 70-1C of the wall 70-1 can be configured as a “free” end,positioned in a radially middle part of the reservoir 36. In theillustrated embodiment, the free end 70-1C is unconnected to inner andouter boundaries of the reservoir 36. During operation of the clutch 20,the shear fluid can migrate between inner and outer sides of the wall70-1 at the end 70-1C under certain circumstances. In this respect, anentrance to (and exit from) the sub-chamber 70 is provided at the end70-1C of the wall 70-1.

The sub-chamber 70 forms a secondary portion of the reservoir 36, whichcan be located along a radially inner part of the reservoir 36. Theshear fluid can enter and exit the sub-chamber 70 only proximate thefree end 70-1C. At least a portion of the shear fluid present in thereservoir 36 can enter the sub-chamber 70, and when the clutch 20 is atrest in an idle condition a volume of the shear fluid can be capturedand retained in the sub-chamber 70. The amount (i.e., percentage) of theshear fluid retained in the sub-chamber 70 will vary as a function ofthe orientation of the free end 70-1C at rest, with greater amounts ofthe shear fluid flowing out of the sub-chamber 70 to another portion ofthe reservoir 36 by means of gravity when the free end 70-1C isrotationally positioned at or near a bottom-dead-center location, thatis, in a lower half of the clutch 20. It should be noted that whilethere is a torque input to the clutch 20, the shear fluid present in thereservoir 36 need not enter the sub-chamber 70 at all, becausecentrifugal forces tend to move any of the shear fluid held in thereservoir 36 into a circumferential band at the outer boundary of thereservoir 36, and the fluid circuit of the clutch 20 does not requirefluid to flow into the sub-chamber 70. Rather, the sub-chamber 70provides a “spur” or secondary fluid path that the shear fluid canenter, typically when the clutch 20 is in an idle condition, and gravityrather than centrifugal force is the primary force acting on the shearfluid.

Further, a wall 70-2 can be provided at a given circumferential locationthat radially spans an entire radial dimension of the reservoir 36, aswell as axially spans an entire axial dimension of the reservoir 36, inorder to block shear fluid flow within the reservoir 36 across the wall70-2 in the circumferential direction. In other words, the shear fluidis blocked by the wall 70-2 and prevented from moving circumferentiallyabout a complete 360° circle within the reservoir 36. In the illustratedembodiment, the wall 70-2 has a planar shape and extends purely radiallywith respect to the axis A. The wall 70-2 can be arranged near the end70-1B of the arcuate segment of the wall 70-1, with a circumferentialspace or gap provided between the end 70-1B of the wall 70-1 and thewall 70-2. The space or gap allows the shear fluid to move radially to“turn” around the end 70-1B of the wall 70-1, such that the shear fluidcan migrate between inner and outer sides of the wall 70-1 to enter thesub-chamber 70 under certain circumstances. Furthermore, the wall 70-2can be positioned adjacent to an inlet portion of the reservoir 36, suchthat the wall 70-2 is located in between the end 70-1B of the wall 70-1and an inlet to the reservoir 36. Because the wall 70-2 can prevent theshear fluid from passing circumferentially to the outlet bore 36-2,additional amounts of the shear fluid can be retained in the reservoir36 by the wall 70-2, with the amount of additionally retained shearfluid depending upon the rotational orientation of the wall 70-2 at restwhen the clutch 20 is in an idle condition.

The walls 70-1 and/or 70-2 can be integrally and monolithically cast ormachined into the base 24-1 of the housing 24. The ability to cast ormachine such structures allows the clutch 20 to be manufactured andassembled relatively easily. Alternatively, the walls 70-1 and/or 70-2can be separate structures attached to the housing 24.

The accumulator 72 can be provided adjacent to (and fluidically upstreamof) the reservoir, and separated from the reservoir 36 by a wall 72-1(e.g., a circumferential wall). In the illustrated embodiment, theaccumulator 72 is located radially inward of the reservoir 36 and isaxially aligned with the reservoir 36, and the wall 72-1 is a shared orcommon separating wall that forms a complete circle and defines both aradially outer boundary of the accumulator 72 and a radially innerboundary of the reservoir 36. The accumulator 72 can be carried by androtationally fixed to the housing 24 (e.g., the base 24-1) or otherinput member of the clutch 20, such that the accumulator 72 co-rotateswith the reservoir 36 at all times (i.e., whenever there is a torqueinput to the clutch 20). A single, radially-oriented bore or port 72-2can be provided in the wall 72-1 that allows the shear fluid to flowsubstantially radially outward from the accumulator 72 to the reservoir36 during clutch operation at a single circumferential location. Inalternate embodiments, the bore 72-2 can have a different orientation,such as an axial orientation. Functionally, the bore 72-2 can beconsidered an inlet bore to the reservoir 36, an outlet bore from theaccumulator 72, and an intermediate bore (with respect to the overallfluid circuit of the clutch 20). Centrifugal forces acting upon theshear fluid allow radially outward flow through the bore 72-2 duringoperation of the clutch 20. Such radially outward flow from theaccumulator 72 to the reservoir 36 is particularly suited to embodimentsof the clutch 20 in which the accumulator 72 (or both the accumulator 72and the reservoir 36) are carried with the input member (e.g., thehousing 24).

The accumulator 72 can have an open face 72-3 in an axial direction. Inthe illustrated embodiment, the open face 70-3 of the accumulator 72faces forward, that is, faces the rotor 26. The open face 72-3 providesa 360° circumferential entrance or inlet to the accumulator 72. Duringoperation, the return bore 26-2 (see FIG. 1) can deliver the shear fluidfrom the working chamber 38 to the accumulator chamber 72 through theopen face. In embodiments where the return bore 26-2 and the accumulator72 are located on different ones of the input and output members (in theillustrated embodiment, the return bore 26-2 is in the output rotor 26and the accumulator 72 is on or carried by the input housing 24), theaccumulator 72 can accept the shear fluid from the return bore 26-2regardless of the relative rotational orientations of the accumulatorand the return bore 26-2. The accumulator 72 in the illustratedembodiment is an annular chamber that has no circumferentialobstructions, and is configured to allow the shear fluid to flow freelythrough an entire circumferential volume.

At least a portion of the shear fluid can be retained in the accumulatorchamber 72 when the clutch 20 is idle to help reduce morning sickness.The amount (i.e., percentage) of the shear fluid retained in theaccumulator 72 will vary as a function of the orientations of the bore72-2 and the return bore 26-2 at rest. In general, greater amounts ofthe shear fluid flowing out of the accumulator 72 to the reservoir 36through the bore 72-2 by means of gravity when the bore 72-2 isrotationally positioned at or near a bottom-dead-center location, thatis, in a lower half of the clutch 20. Moreover, when the return bore26-2 is oriented generally downward at rest, that is, when the returnbore 26-2 is rotationally positioned in the lower half of the clutch 20when at rest in an idle condition, shear fluid in the accumulator 72 candrain back to the working chamber 38. Nonetheless, by allowing the bore72-2 and the return bore 26-2 to have essentially independent rotationalorientations at rest, the clutch 20 can increase the average volume ofthe shear fluid retained by the accumulator 72 over the range ofpossible resting orientations. It should be noted that the accumulatorchamber 72 can be utilized without the sub-chamber 70 in furtherembodiments of the clutch 20. Moreover, one or more additional bores canbe provided between the accumulator 72 and the reservoir 36 in furtherembodiments, though a single bore helps to reduce drain-back effectswhen the clutch 20 is idle. In addition, the open face 72-3 of theaccumulator 72 can be only partially open in alternate embodiments(e.g., open over less than 360°), which may be beneficial if theaccumulator 72 and the reservoir 36 are not rotationally fixed relativeto one another.

Relative internal volumes of the reservoir 36 and the accumulator 72, aswell as for sub-portions of the reservoir 36 such as the sub-chamber(accumulator) 70, can vary as desired for particular applications. Inthe illustrated embodiment, the accumulator 72 has a smaller internalvolume than the reservoir 36.

An axial depth of the reservoir 36 and/or the accumulator 72 can also bevaried to further promote capture and retention of the shear fluid inidle conditions. Such adjustments can allow tailoring of a volume and/orcross-sectional area of the working chamber 38 relative to volumes ofthe reservoir 36 and/or the accumulator 72. For instance, protrusions,grooves, and the like in selected portions of the reservoir could helppromote shear fluid retention at particular angular (i.e.,circumferential) orientations.

Additionally, in alternative embodiments the clutch 20 can include ananti-drainback or morning sickness prevention valve like one disclosedin International patent application Ser. No. PCT/US2016/55260 and U.S.Provisional Patent App. Ser. No. 62/237,286. Various other check valvesknown in the art can also optionally be used with the clutch 20, asdesired for particular applications.

The configuration of the clutch 20 of FIGS. 1 and 2 is provided merelyby way of example and not limitation. Fluid capture systems to reducemorning sickness effects according to the present invention can beutilized in a variety of types of viscous clutches, such that thosehaving different input and output configurations. FIGS. 3 and 4illustrate selected examples of additional clutch configurations, thoughadditional embodiments (not specifically shown) are also contemplated.

FIG. 3 is a cross-sectional view of another embodiment of a viscousclutch 120 that includes a shaft 122, a multi-part housing (or housingassembly) 124, a rotor 126, a valve assembly 132, an electromagnet 134,a reservoir 136, and a working chamber 138. The general operation of theclutch 120 is similar to the clutch 20 described above. However, in theillustrated embodiment, the rotor 126 is affixed to the shaft 122 andprovides a rotational input member for the clutch 120. The housing 124acts as an output member for the clutch 120. The reservoir 136 iscarried by the rotor 126. While the illustrated embodiment has thereservoir 136 on a front side of the clutch 120 (opposite theelectromagnet 134), in further embodiments the reservoir 136 can belocated at a rear side of the rotor 126 or embedded in an axially middleportion of the rotor 126. A return bore 124B extends through the housing124, and delivers the shear pumped from the working chamber to thereservoir 136 via an inlet bore 180. The shear fluid can exit thereservoir 136 and pass to the working chamber to complete a fluidcircuit via an outlet bore 182, which is selectively covered anduncovered by the valve assembly 132. The reservoir can be closed exceptfor the two bores 180 and 182. The clutch 120 omits the accumulator 72of the clutch 20, although such an accumulator can be utilized with theclutch 120 in alternate embodiments.

A wall 170 is provided within the reservoir 136, to separate or divideportions of the reservoir 136 from each other (e.g., generally in theradial direction). Unlike the wall 70-1 of the clutch 20, however, thewall 170 creates an extended, tortuous reservoir path, such that thefluid circuit of the clutch 120 includes the tortuous reservoir path. Inparticular, the wall 170 is positioned in between the bores 180 and 182,such that the shear fluid cannot follow a linear path from the bore 180to the bore 182. The shear fluid passing through the reservoir 136 musttraverse the reservoir path, and the tortuous configuration of thereservoir path lengthens the fluid circuit by extending the fluidcircuit (e.g., in a circumferential direction), which helps to captureand retain at least a portion of the shear fluid held in the reservoir136 when the clutch 120 is in an idle condition. The shape of the wall170 and the placement of the bores 180 and 182 helps ensure that asubstantial amount of the shear fluid is captured in the reservoir 136when the clutch 120 is shut down (i.e., “off” or in an idle condition)regardless of the angular orientation of the clutch components at rest.The tortuous reservoir path is explained further below (see, forexample, the discussion with respect to FIG. 7). However, in alternateembodiments the sub-chamber 70 and/or the accumulator 72 of the clutch20 can be utilized with the clutch 120 instead of the wall 170, forinstance.

To further promote capture and retention of the shear fluid, bores 180and 182 can be angularly offset from each other (i.e., in acircumferential direction) to help maintain independent fluid paths.

FIG. 4 is a cross-sectional view of another embodiment of a viscousclutch 220 that includes a shaft 222, a multi-part housing (or housingassembly) 224, a rotor 226, a valve assembly 232, an electromagnet 234,a reservoir 236, and a working chamber 238. The general operation of theclutch 220 is similar to the clutches 20 and 120 described above, andcan resemble the clutch described in commonly-assigned U.S. PatentApplication Publication No. 2015/0240888. However, in the illustratedembodiment, the clutch 220 utilizes a static (i.e., non-rotating) shaft222. The housing 224 can function as an input member of the clutch 220,and the rotor 226 can function as an output member. The rotor 226 caninclude a hub 226-1 that protrudes out of the housing 224 to enableattachment of an output device, such as a fan (not shown). Furthermore,the housing 224 can include a pulley 224-1 to connect to a torque inputsource.

A return bore 226-2 is provided in the rotor 226, to deliver fluidpumped from the working chamber 238 along a fluid circuit toward thereservoir 236.

A reservoir plate 236-1 is provided and forms a portion of a boundary ofthe reservoir 236. An outlet bore 236-2 and an inlet bore 236-3 areprovided through the plate 236-1. Although a gap at the inlet bore 236-3means that the reservoir 236 is not closed, that is there is anadditional opening from the reservoir 236, such a gap is relativelyclose to an axis A of the clutch 220, which tends to lessen morningsickness drainback. A seal (not shown) can be added at the gap infurther embodiments, as desired, to provide a closed reservoir.

A wall 270 is provided within the reservoir 236, to separate or divideportions of the reservoir 236 from each other (e.g., generally in theradial direction). Like the wall 170, the wall 270 creates an extended,tortuous reservoir path, such that the fluid circuit of the clutch 220includes the tortuous reservoir path. In particular, the wall 270 ispositioned in between the bores 236-2 and 236-3, such that the shearfluid cannot follow a linear path from the inlet bore 236-2 to theoutlet bore 236-3. The shear fluid passing through the reservoir 236must traverse the reservoir path, and the tortuous configuration of thereservoir path lengthens the fluid circuit by extending or lengtheningthe fluid circuit (e.g., in a circumferential direction), which helps tocapture and retain at least a portion of the shear fluid held in thereservoir 236 at one or more locations along the reservoir path when theclutch 220 is in an idle condition. The shape of the wall 270 and theplacement of the bores 236-2 and 236-3 helps ensure that a substantialamount of the shear fluid is captured in the reservoir 236 when theclutch 220 is shut down (i.e., “off” or in an idle condition) regardlessof the angular orientation of the clutch components at rest. Thetortuous reservoir path is explained further below (see, for example,the discussion with respect to FIG. 7). However, in alternateembodiments the sub-chamber 70 and/or the accumulator 72 of the clutch20 can be utilized with the clutch 220 instead of the wall 270, forinstance.

FIGS. 5-11 are schematic views of different embodiments of a viscousfluid capture system for a viscous clutch. Retained shear fluid is shownin FIGS. 5-11 as stippling, for illustrative purposes. For simplicity,FIGS. 5-11 show only fluid capture system embodiments in isolation,without other components of the viscous clutch (as shown in FIGS. 1-4).It should be understood that the embodiments of the fluid capture systemof FIGS. 5-11 can be implemented in a variety of overall viscous clutchdesigns, such as those resembling the example viscous clutches shown inFIGS. 1-4 or other types not specifically shown, and can be implementedon input or output members of a viscous clutch, as desired forparticular applications.

FIG. 5 is a schematic view of an embodiment of a fluid capture system500 for use with a viscous clutch. The system 500 includes anaccumulator 502, a reservoir 504, walls 506 and 508, and bores 510 and512.

The accumulator 502 can be a generally annular chamber that accepts ashear fluid from a working chamber via a return bore (not shown in FIG.5). The accumulator 502 can have an open face as an inlet, or anothertype of inlet bore. The shear fluid can pass from the accumulator 502 tothe reservoir 504 via the bore 510, which, in the illustratedembodiment, is oriented radially with the accumulator located radiallyinward of the reservoir 504. The bore 510 can be the only passagewaybetween the accumulator 502 and the reservoir 504, such that only asingle fluid path at a single location links the accumulator 502 and thereservoir 504 in series along a clutch fluid circuit.

The reservoir 504 has an inner boundary 504A and an outer boundary 504B,and includes a sub-chamber defined at least in part by the wall 506,which can extend axially across an entire dimension of the reservoir 504to provide a fluid-tight barrier. The wall 506 has a main body (orsegment) 506B and opposite ends 506-1 and 506-2, and can be at leastpartially arcuate in shape (e.g., the main body 506B can be arcuate),extending about an axis A of the clutch over an angular range β. In theillustrated embodiment, the angular range β is approximately 315°,though other angular ranges can be used in alternate embodiments. Themain body 506B can be located in a radially intermediate or middleportion of the reservoir 504. A projection 506-3 extends radially inwardfrom the main body 506B of the wall 506 at or near the end 506-1, andpreferably at the end 506-1. The projection 506-3 extends to the innerboundary 504A of the reservoir 504, forming a “dead end” in thesub-chamber formed by the wall 506. The wall 508 extends radially acrossthe entire reservoir 504, from the inner boundary 504A to the outerboundary 504B, and is positioned adjacent to the end 506-2 of the wall506, separated from the end 506-2 by a gap. In the illustratedembodiment, the bore 510 is positioned in between the ends 506-1 and506-2, and in between the projection 506-3 and the wall 508, in anangular or circumferential direction. An area of the reservoir 504adjoining the bore 510 can be considered an inlet portion of thereservoir 504.

The bore 512 can be located adjacent to the bore 510. The bore 512 canbe located in a reservoir plate, and can be oriented generally normal tothe bore 510 (e.g., the bore 512 can extend substantially axially). Thebore 512 provides an outlet from the reservoir 504, such that the shearfluid can pass out of the reservoir 504 toward the working chamber (notshown) to continue along the fluid circuit. In the illustratedembodiment, the bores 510 and 512 are located in a common angularquadrant of the reservoir 504 (relative to the axis A), and morespecifically can be located within approximately 15° of each other. Thebore 512 can further be located in between the projection 506-3 and thewall 508. The bores 510 and 512 can be the only inlets/outlets to anotherwise closed and sealed reservoir 504.

When a clutch having the system 500 is in an idle condition, the shearfluid that is in the reservoir 504 can potentially drain back to theworking area through either of the bores 510 or 512. In a typical priorart clutch, if either bore is oriented downward, it is easy for most ofthe shear fluid to drain back from the reservoir to the working chamber.However, because the sub-chamber formed by the wall 506 and/or the wall508 can capture and retain some of the shear fluid, the system 500 helpsretain shear fluid in the reservoir 504 and limit how much shear fluidis able to drain back to the working chamber out of either bore 510 or512 by way of gravity when the system 500 is at rest. The accumulator502 can further help reduce drainback of the shear fluid to the workingchamber.

As shown in FIG. 5, the shear fluid is retained within the reservoir 504by the walls 506 and 508. In the illustrated orientation, the shearfluid is able to drain out of the accumulator 502 to the reservoir 504,but in other angular orientations a portion of the shear fluid would beretained in the accumulator 502 as well.

FIG. 6 is a schematic view of an embodiment of a fluid capture system600 for use with a viscous clutch. The system 600 includes anaccumulator 602, a reservoir 604, walls 606 and 608, and bores 610 and612. The reservoir 604 has an inner boundary 604A and an outer boundary604B, and includes a sub-chamber defined at least in part by the wall606. The wall 606 has a main body (or segment) 606B and opposite ends606-1 and 606-2, and can be at least partially arcuate in shape (e.g.,the main body 606B can be arcuate), extending about an axis A of theclutch over an angular range β.

The configuration and operation of the system 600 is generally similarto the system 500 described with respect to FIG. 5; however, the angularrange β of the wall 606 is approximately 170° and the bore 612 islocated more radially inward than the bore 512. The embodiment of thesystem 600 provides a lower mass, due to a shorter wall 606, and alarger gap between the end 606-2 and the wall 608 to facilitate flow ofthe shear fluid. Although the wall 606 will retain less of the shearfluid than the wall 506 at some angular orientations, in the illustratedorientation the systems 500 and 600 capture and retain comparablevolumes of the shear fluid, with the alternate location of the bore 612providing a small increase in shear fluid retention in the system 600over the system 500. A further trade-off between the embodiments ofFIGS. 5 and 6, is that the more radially outward bore 512 can helpincrease clutch response time slightly, due to centrifugal forces actingon the shear fluid during operation.

FIG. 7 is a schematic view of an embodiment of a fluid capture system700 for use with a viscous clutch. The system 700 includes anaccumulator 702, a reservoir 704, a wall 706, and bores 710 and 712.Unlike the embodiments of systems 500 and 600 that primarily seek tocapture and retain a shear fluid away from a working chamber in asub-compartment or sub-chamber that is peripheral to a clutch fluidcircuit, the system 700 provides a tortuous reservoir path 714 thatextends a length of a fluid circuit to help retain and capture the shearfluid away from the working chamber.

The accumulator 702 can be a generally annular chamber that accepts theshear fluid from the working chamber via a return bore (not shown inFIG. 7). The accumulator 702 can have an open face as an inlet, oranother type of inlet bore. The shear fluid can pass from theaccumulator 702 to the reservoir 704 via the bore 710, which, in theillustrated embodiment, is oriented radially with the accumulator 702located radially inward of the reservoir 704. The bore 710 can be theonly passageway between the accumulator 702 and the reservoir 704, suchthat only a single fluid path at a single location links the accumulator702 and the reservoir 704 in series along the clutch fluid circuit.Additionally, the bores 710 and 712 can be the only inlets/outlets to anotherwise sealed reservoir 704.

The reservoir 704 has an inner boundary 704A and an outer boundary 704B.The bore 710 can be located at or near an inner diameter (ID) of thereservoir 704, such as at the inner boundary 704A, and the bore 712 canbe located at or near an outer diameter (OD) of the reservoir 704, suchas near but radially inward from the outer boundary 704B. The bore 712can be located in a reservoir plate, and can be oriented generallynormal to the bore 710 (e.g., the bore 712 can extend substantiallyaxially). An area of the reservoir 704 adjoining the bore 710 can beconsidered an inlet portion of the reservoir 704. The bore 712 providesan outlet from the reservoir 704, such that the shear fluid can pass outof the reservoir 704 toward the working chamber (not shown) to continuealong the fluid circuit. Because rotation of the reservoir 704 duringoperation tends to move the shear fluid to the OD of the reservoir 704by centrifugal forces, the OD location of the bore 712 allows forrelatively quick delivery of the shear fluid from the reservoir 704 tothe working chamber when a clutch valve assembly is actuated. The bores710 and 712 can be located at an angle a from one another, relative tothe rotational axis A. The angle a can be approximately 180°, or alarger or smaller angle in alternative embodiments.

The reservoir 704 includes a fluid-tight barrier or dividing structuredefined wholly or partially by the wall 706, which can extend axiallyacross an entire dimension of the reservoir 704. The wall 706 has a mainbody (or segment) 706B and opposite ends 706-1 and 706-2, and can be atleast partially arcuate in shape, extending about the axis A over anangular range β. The main body 706B can be located in a radiallyintermediate or middle portion of the reservoir 704, and can have ahelically outward progression from the end 706-1 to the opposite end706-2. In the illustrated embodiment, the angular range β isapproximately 180°, though other angular ranges can be used in alternateembodiments. A projection (or end piece) 706-3 extends radially inwardfrom the main body 706B of the wall 706 at or near the end 706-1, andpreferably at the end 706-1, to the inner boundary 704A of the reservoir704. A projection (or end piece) 706-4 extends radially outwardly fromthe main body 706B of the wall 706 at or near the end 706-2, to theouter boundary 704B of the reservoir 704. In this way, the projections706-3 and 706-4 extend in opposite radial directions relative to themain body 706B of the wall 706. The projection 706-4 can have a convexshape in an angular or circumferential direction (e.g., with theconvexity protruding away from the bore 712). In the illustratedembodiment, the bore 710 is positioned adjacent and proximate to the end706-1 and the projection 706-3 of the wall 706, and the bore 712 ispositioned adjacent and proximate to the end 706-2 and the projection706-4 of the wall 706. The projections 706-3 and 706-4 can both belocated to the same side of a projected line 716 that passes throughcenters of the bores 710 and 712. Described another way, the wall 706can have a “C”-shape with serif-like projections 706-3 and 706-4 ateither ends 706-1 and 706-2 that both protrude radially in the samedirection (e.g., downward as illustrated in FIG. 7).

As shown in the illustrated embodiment of FIG. 7, a first portion of thereservoir 704 has a first “dead end” portion proximate the projection706-3 and the bore 710 and radially inward from the wall 706, and asecond portion of the reservoir 704 has a second “dead end” portionproximate the projection 706-4 and the bore 712 and radially outwardfrom the wall 706. In this way, the dividing structure creates thetortuous (e.g., spiral or snail-shell) shaped reservoir path 714 betweenthe bores 710 and 712. The reservoir path 714 can traverse or sweep overan angular range θ, about the axis A. In the illustrated embodiment, theangular range θ is approximately 540°. Furthermore, in the illustratedembodiment, θ≥3α. In alternate embodiments, the angular range θ can belarger or smaller, such as with θ≥360° or θ>180°. Furthermore, in someembodiments, θ≥α, and preferably θ>α, and more preferably θ>>α. Duringoperation, the shear fluid is forced to travel along the reservoir path714 through the entire angular range θ to go from the entrance/inlet(i.e., the bore 710) to the exit/outlet (i.e., the bore 712) and therebypass through the reservoir 704 along the fluid circuit.

When a clutch having the system 700 is in an idle or “off” condition,the shear fluid in the reservoir 704 can potentially drain back to theworking area through either of the bores 710 or 712. In a typical priorart clutch, if either bore is oriented downward, it is easy for most ofthe shear fluid to drain back from the reservoir to the working chamber.However, because the two bores 710 and 712 are located at the angle a(e.g., approximately 180°) from one another, and the reservoir path 714traverses the angular range of θ, only one bore (710 or 712) can beoriented downward (i.e., located below a horizontal projected line thatpasses through the axis A) at any given time. Furthermore, the wall 706helps retain shear fluid in the reservoir 704, and limit how much shearfluid is able to drain back to the working chamber out of either bore710 or 712 by way of gravity when the system 700 is at rest. In theupstream-downstream direction, a middle portion of the reservoir path714 has a radial dimension that extends from the inner boundary 704A tothe outer boundary 704B, without any narrowing or obstruction by thewall 706, which allows a relatively large volume of the shear fluid tobe captured and retained at the middle portion of the reservoir path 714during idle conditions.

FIG. 8 is a schematic view of an embodiment of a fluid capture system800 for use with a viscous clutch. The system 800 includes anaccumulator 802, a reservoir 804, a wall 806, and bores 810 and 812. Thereservoir 804 has an inner boundary 804A and an outer boundary 804B. Thebores 810 and 812 can be located at an angle a from one another,relative to a rotational axis A. The wall 806 has a main body (orsegment) 806B and opposite ends 806-1 and 806-2, and can be at leastpartially arcuate in shape, extending about the axis A over an angularrange β. In the illustrated embodiment, the main body 806B has a spiralor helical shape, progressing helically outward from the end 806-1 tothe opposite end 806-2. A projection 806-3 extends radially inward fromthe main body 806B of the wall 806 at or near the end 806-1, andpreferably at the end 806-1, to the inner boundary 804A of the reservoir804. A projection 806-4 extends radially outwardly from the main body806B of the wall 806 at or near the end 806-2, to the outer boundary804B of the reservoir 804. The projections 806-3 and 806-4 can belocated on the same side of a projected line 816 connecting centers ofthe bores 810 and 812. A reservoir path 814 from the bore 810 to thebore 812 can traverse or sweep over an angular range θ, about the axisA.

The system 800 has a configuration generally similar to the system 700,with the wall 806 providing the tortuous reservoir path 814 that extendsa length of a fluid circuit to help retain and capture the shear fluidaway from a working chamber. However, the wall 806 is longer than thewall 706, such that the wall 806 wraps around the axis A more than onceand overlaps itself in the angular or circumferential direction. Moreparticularly, in the illustrated embodiment, the angular range θ isapproximately 540°. Similar to the system 700, during operation of thesystem 800, the shear fluid is forced to travel along the reservoir path814 through the entire angular range θ to go from the entrance/inlet(i.e., the bore 810) to the exit/outlet (i.e., the bore 812) and therebypass through the reservoir 804 along the fluid circuit. Because thebores 810 and 812 are located at the angle a (e.g., approximately 180°)from one another, and the reservoir path 814 traverses the angular rangeof θ (e.g., with θ>α), only one bore (810 or 812) can be orienteddownward (i.e., located below a horizontal projected line that passesthrough the axis A) at any given time. Furthermore, the wall 806 helpsretain shear fluid in the reservoir 804, and limit how much shear fluidis able to drain back to the working chamber out of either bore 810 or812 by way of gravity when the system 800 is at rest.

FIG. 9 is a schematic view of an embodiment of a fluid capture system900 for use with a viscous clutch. The system 900 includes anaccumulator 902, a reservoir 904, a wall 906, and bores 910 and 912. Thereservoir 904 has an inner boundary 904A and an outer boundary 904B. Thebores 910 and 912 can be located at an angle a (e.g., approximately180°) from one another, relative to a rotational axis A. The wall 906has a main body (or segment) 906B and opposite ends 906-1 and 906-2, andcan be at least partially arcuate in shape, extending about the axis Aover an angular range β. In the illustrated embodiment, the main body906B has a partially spiral or helical shape, with an upstream portion(closest to the end 906-1) progressing helically outward from the end906-1 toward the opposite end 906-2, and with a downstream portion(closest to the end 906-2) configured as a non-helical, circular arcsegment. The helical portion of the main body 906B meets the circularportion of the main body 906B at a point 906H. A projection 906-3extends radially inward from the main body 906B of the wall 906 at ornear the end 906-1, and preferably at the end 906-1, to the innerboundary 904A of the reservoir 904. A projection 906-4 extends radiallyoutwardly from the main body 906B of the wall 906 at or near the end906-2, to the outer boundary 904B of the reservoir 904. The projections906-3 and 906-4 can be located on the same side of a projected line 916connecting centers of the bores 910 and 912. In the illustratedembodiment, the projection 906-4 includes a substantially planar portionjoined to the arcuate main body 906B by a radiused, convex corner thatprotrudes radially inward from the adjacent region of the main body906B. The inwardly protruding shape of the radiused corner can help tofurther capture and retain the shear fluid at particular angularorientations of the system 900, by discouraging the shear fluid fromeasily flowing past the protrusion along an inner side of the wall 906.A reservoir path 914 from the bore 910 to the bore 912 can traverse orsweep over an angular range θ (e.g., approximately 540°), about the axisA.

The system 900 has a configuration generally similar to the systems 700and 800, with the wall 906 providing the tortuous reservoir path 914that extends a length of a fluid circuit to help retain and capture theshear fluid away from a working chamber. However, unlike the helicalmain body 806B of the system 800, the main body 906B of the wall 906 isonly partially helical, with an upstream helical portion and adownstream circular (non-helical) portion. A varying cross-sectionalarea of the reservoir path 914 created by the helical/non-helical shapeof the main body 906B of the wall 906 helps to tailor shear fluidcapture and retention functionality. For instance, a cross-sectional areand volume of portions of the reservoir 904 can be larger at a middleportion of the reservoir path 914 than at both an upstream end and adownstream end of the reservoir path 914. Moreover, thehelical/non-helical shape more aggressively forces the shear fluidtoward the outside of the reservoir 904 during rotation. This will helpthe shear fluid move from the ID to the OD quicker, to help improveclutch response times. Similar to the systems 700 and 800, duringoperation of the system 900, the shear fluid is forced to travel alongthe reservoir path 914 through the entire angular range θ to go from theentrance/inlet (i.e., the bore 910) to the exit/outlet (i.e., the bore912) and thereby pass through the reservoir 904 along the fluid circuit.Because the bores 910 and 912 are located at the angle a (e.g.,approximately 180°) from one another, and the reservoir path 914traverses the angular range θ (e.g., with θ>α), only one bore (910 or912) can be oriented downward (i.e., located below a horizontalprojected line that passes through the axis A) at any given time.Furthermore, the wall 906 helps retain shear fluid in the reservoir 904,and limit how much shear fluid is able to drain back to the workingchamber out of either bore 910 or 912 by way of gravity when the system900 is at rest.

FIG. 10 is a schematic view of an embodiment of a fluid capture system1000 for use with a viscous clutch. The system 1000 includes anaccumulator 1002, a reservoir 1004, a wall 1006, and bores 1010 and1012. The reservoir 1004 has an inner boundary 1004A and an outerboundary 1004B, and can optionally include one or more portions with anincreased axial depth. The bores 1010 and 1012 can be located at anangle a from one another, relative to a rotational axis A. The angle acan be relatively small, such as less than 90°, less than 45°, orpreferably approximately 30°. The wall 1006 has a main body (or segment)1006B and opposite ends 1006-1 and 1006-2, and can be at least partiallyarcuate in shape, extending about the axis A over an angular range β. Areservoir path 1014 from the bore 1010 to the bore 1012 can traverse orsweep over an angular range θ (e.g., approximately 330°), about the axisA.

In the illustrated embodiment, the main body 1006B has a partiallyspiral or helical shape, with an upstream portion (closest to the end1006-1) and a downstream portion (closest to the end 1006-2) beingcircular (i.e., non-helical), with a middle portion of the main body1006B progressing helically outward from a first point 1006H to a secondpoint 1006H′ along the main body 1006B. Such a configuration allowsupstream and downstream portions of the reservoir 1004 (along thereservoir path 1014) to have relatively small volumes, while a middleportion of the reservoir 1004 (along the reservoir path 1014) can have arelatively large volume to help retain the shear fluid under idleconditions. In this respect, the upstream portion of the main body 1006B(near the end 1006-1) is relatively close to the inner boundary 1004Aand the upstream portion of the main body 1006B (near the end 1006-2) isrelatively close to the outer boundary 1004B.

A projection 1006-3 extends radially inward from the main body 1006B ofthe wall 1006 at or near the end 1006-1, and preferably at the end1006-1, to the inner boundary 1004A of the reservoir 1004. A projection1006-4 extends radially outwardly from the main body 1006B of the wall1006 at or near the end 1006-2, to the outer boundary 1004B of thereservoir 1004. In the illustrated embodiment, the projection 1006-4includes a substantially planar portion joined to the arcuate main body1006B by a radiused, convex corner that protrudes radially inward fromthe adjacent region of the main body 1006B. Further, as shown in theillustrated embodiment, a generally radial notch or groove can beprovided at the bore 1010, in a common wall separating the accumulator1002 from the reservoir 1004, to help increase a volume of an inletportion of the reservoir 1004 and to move the bore 1010 further fromregions of the reservoir 1004 where the shear fluid is retained when theclutch is in the idle condition.

The system 1000 has a configuration generally similar to the systems700, 800 and 900, with the wall 1006 providing the tortuous reservoirpath 1014 that extends a length of a fluid circuit to help retain andcapture the shear fluid away from a working chamber. Likewise, similarto the systems 700, 800 and 900, during operation of the system 1000,the shear fluid is forced to travel along the reservoir path 1014through the entire angular range θ to go from the entrance/inlet (i.e.,the bore 1010) to the exit/outlet (i.e., the bore 1012) and thereby passthrough the reservoir 1004 along the fluid circuit. However, the angularrange θ for the system 1000 is larger, approaching 360°. Although it ispossible for both of the bores 1010 and 1012 to be oriented downward(i.e., located below a horizontal projected line that passes through theaxis A) under some idle conditions, the likelihood of shear fluiddrainback is offset by the relatively longer reservoir path 1014. Aswith the previously-discussed embodiments, the wall 1006 helps retainshear fluid in the reservoir 1004, and limit how much shear fluid isable to drain back to the working chamber out of either bore 1010 or1012 by way of gravity when the system 1000 is at rest.

FIG. 11 is a schematic view of an embodiment of a fluid capture system1100 for use with a viscous clutch. The system 1100 includes anaccumulator 1102, a reservoir 1104, walls 1106 and 1108, and bores 1110and 1112. Unlike the embodiments of systems 500 and 600 that primarilyseek to capture and retain a shear fluid away from a working chamber ina sub-compartment or sub-chamber that is peripheral to a clutch fluidcircuit, the system 1100 provides a tortuous reservoir path 1114 thatextends a length of a fluid circuit to help retain and capture the shearfluid away from the working chamber.

The accumulator 1102 can be a generally annular chamber that accepts theshear fluid from the working chamber via a return bore (not shown inFIG. 11). The accumulator 1102 can have an open face as an inlet, oranother type of inlet bore. The shear fluid can pass from theaccumulator 1102 to the reservoir 1104 via the bore 1110, which, in theillustrated embodiment, is oriented radially with the accumulator 1102located radially inward of the reservoir 1104. The bore 1110 can be theonly passageway between the accumulator 1102 and the reservoir 1104,such that only a single fluid path at a single location links theaccumulator 1102 and the reservoir 1104 in series along the clutch fluidcircuit. Additionally, the bores 1110 and 1112 can be the onlyinlets/outlets to an otherwise closed and sealed reservoir 1104.

The reservoir 1104 has an inner boundary 1104A and an outer boundary1104B. The bore 1110 can be located at or near the ID of the reservoir1104, such as at the inner boundary 1104A, and the bore 1112 can belocated at or near an OD of the reservoir 1104, such as near butradially inward from the outer boundary 1104B. The bore 1112 can belocated in a reservoir plate, and can be oriented generally normal tothe bore 1110 (e.g., the bore 1112 can extend substantially axially). Anarea of the reservoir 1104 adjoining the bore 1110 can be considered aninlet portion of the reservoir 704. The bore 1112 provides an outletfrom the reservoir 1104, such that the shear fluid can pass out of thereservoir 1104 toward the working chamber (not shown) to continue alongthe fluid circuit. Because rotation of the reservoir 1104 duringoperation tends to move the shear fluid to the OD of the reservoir 1104by centrifugal forces, the OD location of the bore 1112 allows forrelatively quick delivery of the shear fluid from the reservoir 1104 tothe working chamber when a clutch valve assembly is actuated. The bores1110 and 1112 can be located at an angle a relative to one another, withrespect to the rotational axis A. The angle a can be approximately 0°,meaning that the bores 1110 and 112 are substantially aligned at acommon angular (or circumferential) location, or can be a larger anglein alternative embodiments.

The reservoir 1104 includes a dividing structure defined by the walls1106 and 1108, which can each extend axially across an entire dimensionof the reservoir 1104 to create respective fluid-tight barriers. Thewall 1106 has a main body (or segment) 1106B and opposite ends 1106-1and 1106-2, and can be at least partially arcuate in shape, extendingabout the axis A over an angular range β₁. The wall 1108 has a main body(or segment) 1108B and opposite ends 1108-1 and 1108-2, and can be atleast partially arcuate in shape, extending about the axis A over anangular range β₂. The angular ranges β₁ and β₂ can each be relativelylarge, such as being greater than or equal to 180°, greater than orequal to 270°, greater than or equal to 330°, or approaching 360°. Inthe illustrated embodiment, the angular range β₁ is approximately 330°and the angular range β₂ is approximately 340°, though other angularranges can be used for either angular range in alternate embodiments.

The main bodies 1106B and 1108B can each be located in a radiallyintermediate or middle portion of the reservoir 1104. In the illustratedembodiment, the main body 1106B of the wall 1106 is located radiallyinward of the main body 1108B of the wall 1108. Moreover, as shown inthe illustrated embodiment, the wall 1106 can be positioned (radially)closer to the inner boundary 1104A of the reservoir 1104 than to thewall 1108, and the wall 1108 can be positioned (radially) closer to theouter boundary 1104B of the reservoir 1104 than to the wall 1106.

A projection (or end piece) 1106-3 extends radially inward from the mainbody 1106B of the wall 1106 at or near the end 1106-1, and preferably atthe end 1106-1, to the inner boundary 1104A of the reservoir 1104. Theend 1106-2 can be configured as a free end, which terminates in aradially middle portion of the reservoir 1104, spaced from the inner andouter boundaries 1104A and 1104B. In the illustrated embodiment, thebore 1110 is positioned adjacent and proximate to the end 1106-1 and theprojection 1106-3 of the wall 1106.

A projection (or end piece) 1108-3 extends radially outward from themain body 1108B of the wall 1108 at or near the end 1108-1, andpreferably at the end 1108-1, to the outer boundary 1104B of thereservoir 1104. The end 1108-2 can be configured as a free end, whichterminates in a radially middle portion of the reservoir 1104, spacedfrom the inner and outer boundaries 1104A and 1104B. In the illustratedembodiment, the bore 1112 is positioned adjacent and proximate to theend 1108-1 and the projection 1108-3 of the wall 1108.

The projections 1106-3 and 1108-3 can be located on opposite sides of aprojected line 1116 that passes through the centers of the bores 1110and 1112. The free ends 1106-2 and 11-8-2 can also be located onopposite sides of the projected line 1116. Furthermore, the projection1106-3 and the free end 1106-2 can be located on the same side of theprojected line 1116, and the projection 1108-3 and the free end 1108-2can be located on the same side of the projected line 1116 (e.g., acommon circumferential location of the bores 1110 and 1112).

As shown in the illustrated embodiment of FIG. 11, one portion of thereservoir 1104 has a “dead end” portion proximate the projection 1106-3and the bore 1110, radially inward from the wall 1106, and anotherportion of the reservoir 1104 has another “dead end” portion proximatethe projection 1108-3 and the bore 1112, radially outward from the wall1108. A middle portion 1118 is located radially in between the walls1106 and 1108, and separated from the bores 1110 and 1112 by the walls1106 and 1108 (and the associated dead-end portions). In this way, thedividing structure of the system 1100 creates the tortuous shapedreservoir path 1114 between the bores 1110 and 1112. The reservoir path1114 can traverse or sweep over a minimum angular range θ, about theaxis A. In the illustrated embodiment, the angular range θ isapproximately 720°. Furthermore, in the illustrated embodiment,θ≥(β₁+β₂). In alternate embodiments, the angular range θ can be largeror smaller. During operation, the shear fluid is forced to travel alongthe reservoir path 1114 through the entire minimum angular range θ to gofrom the entrance/inlet (i.e., the bore 1110) to the exit/outlet (i.e.,the bore 1112) and thereby pass through the reservoir 1104 along thefluid circuit. At least part of the middle portion 1118 is unobstructedin a circumferential direction. Because the middle portion 1118 allowsthe shear fluid to flow generally radially past the free ends 1106-2 and1108-2, but also allows the shear fluid to continue to flow tangentiallyor circumferentially around the middle portion 1118, the reservoir path1114 has only a minimum angular range θ, and the shear fluid cancirculate further in the middle portion over a larger angular range(which can be expressed as θ+n*360, wherein n is a non-negativeinteger).

As with previously-described embodiments, the system 1100 allows for thetortuous reservoir path 1114 to facilitate capture and retention of theshear fluid in an idle condition, facilitated by the walls 1106 and1108.

The various embodiments of the present invention provide numerousadvantages and benefits. For instance, shear fluid retention and capturecan be provided passively, without the need for any moving elements(such as valves), pumping of the shear fluid within the reservoir orbetween the accumulator and the reservoir, or other active orquasi-active mechanisms. Various embodiments of the invention canutilize an accumulator in addition to structures within a reservoir. Thedividing structure(s) within the reservoir according to embodiments ofthe present invention also do not require a radial or axial enlargementof the reservoir, which helps maintain a compact clutch design. The useof multiple features for shear fluid capture and retention has beenfound to provide benefits in terms of reduced morning sickness drainbackeffects, without having a significant negative impact on clutchperformance when a torque input is present. In other words, while theuse of morning-sickness reduction/prevention features, and especiallymultiple morning sickness features, presents a risk of adverse impactsupon clutch engagement and/or disengagement response times, clutch axialand/or radial size, manufacturing and assembly complexity, overallclutch mass, and other aspects, the present invention allows for afavorable trade-off between those considerations. The clutch and fluidcapture system of the present invention provides a favorable tradeoffbetween clutch size and mass, manufacturability, and “morning sickness”mitigation. Other morning sickness prevention mechanisms require stackedor nested chambers that complicate clutch manufacture and tend toincrease clutch size and mass, especially in an axial direction. While adegree of oil capture/retention according to embodiments of the presentinvention still varies depending on orientation of clutch in an idlestate, retention of more than 45% of a total shear fluid volume has beenfound across all idle angular orientations, with over 85% shear fluidretention in some angular orientations for some embodiments and medianfluid retention of roughly 65% across all angular orientations for mostembodiments.

Discussion of Possible Embodiments

The following are non-exclusive descriptions of possible embodiments ofthe present invention.

A viscous clutch can include an input member; an output member; aworking chamber defined between the input member and the output member;a reservoir to hold a supply of a shear fluid, the reservoir fluidicallyconnected to the working chamber by a fluid circuit; an outlet to passthe shear fluid from the reservoir to the working chamber along thefluid circuit; a return bore to return the shear fluid pumped out of theworking chamber along the fluid circuit; an accumulator to accept theshear fluid from the return bore, wherein the accumulator is arranged inseries with the reservoir in the fluid circuit; and a first wall havingan arcuate segment, the first wall positioned within the reservoir toseparate a first portion of the reservoir from a second portion of thereservoir.

The viscous clutch of the preceding paragraph can optionally include,additionally and/or alternatively, any one or more of the followingfeatures, configurations and/or additional components:

the reservoir can be carried by the input member;

the input member can comprise a housing, and the output member cancomprise a rotor disk;

the accumulator can have an axially open face;

a radial wall extending across an entire radial dimension of thereservoir from an inner boundary to an outer boundary, the radial wallbeing spaced from the first wall and configured to preventcircumferential movement of the shear fluid across a circumferentiallocation of the radial wall;

the accumulator can be located upstream of the reservoir, between thereturn bore and the reservoir, in the fluid circuit of the viscousclutch;

the accumulator can be located radially inward of the reservoir;

the accumulator can be configured as an annular chamber;

the accumulator can be configured to allow the shear fluid to flowfreely through an entire circumferential volume;

a reservoir plate positioned along a boundary of the reservoir, thereservoir plate extending radially, wherein the outlet is configured asa bore in the reservoir plate configured to allow the shear fluid topass from the reservoir to the working chamber along the fluid circuit;

a separating wall between the accumulator and the reservoir;

an intermediate bore in the separating wall to allow the shear fluid topass from the accumulator to the reservoir along the fluid circuit,wherein the intermediate bore is oriented normal to the bore of theoutlet in the reservoir plate;

an intermediate bore connecting the accumulator to the reservoir alongthe fluid circuit, wherein the outlet is configured as a bore in aboundary of the reservoir, and wherein the intermediate bore is orientednormal to the bore of the outlet.

a valve assembly configured to regulate flow of the shear fluid alongthe fluid circuit;

the arcuate segment of the first wall can extend about an angular rangeβ with respect to an axis of the viscous clutch, the angular range βbeing greater than 180°;

the arcuate segment of the first wall can extend about an angular rangeβ with respect to an axis of the viscous clutch, the angular range βbeing greater than 360°;

the reservoir can be configured with an inlet portion circumferentiallyspaced from an outlet bore by approximately 180°;

the fluid circuit can include a reservoir path that traverses an angularrange of at least 540°;

the first wall can further include a first end projection that radiallyconnects the arcuate segment to a first circumferentially-extendingboundary of the reservoir;

the first wall further can further include a second end projection thatradially connects the arcuate segment to a secondcircumferentially-extending boundary of the reservoir, and the secondend projection can be located opposite the first end projection alongthe arcuate segment;

a second wall can have an arcuate segment, and the second wall can bepositioned within the reservoir radially adjacent to the first wall toseparate a third portion of the reservoir from the first and secondportions of the reservoir;

the reservoir can have a first bore and a second bore, the first boreproviding an inlet to the reservoir along the fluid circuit and thesecond bore providing the outlet from the reservoir along the fluidcircuit, and wherein the first and second bores are aligned at a commoncircumferential location;

the first and second walls can each have a free end, and the free endscan be arranged on opposite sides of the common circumferentiallocation;

at least a portion of the arcuate segment of the first wall can have ahelical shape;

the arcuate segment of the first wall can have a circular portion at adownstream end proximate an outlet bore of the reservoir, and ahelically-shaped portion of the arcuate segment can be located upstreamof the circular portion;

the fluid circuit can include a reservoir path through the reservoir,and wherein a cross-sectional area of the reservoir varies along thereservoir path;

a cross-sectional area of the reservoir can be larger at a middleportion of the reservoir path than at both an upstream end and adownstream end of the reservoir path;

the accumulator and the reservoir can be arranged at a common axiallocation; and/or

at least a portion of the return bore can extend radially.

A method for use with a viscous clutch can include pumping a shear fluidradially inward from a working chamber to an accumulator; passing theshear fluid from the accumulator to a reservoir having a closedconfiguration; separating a first portion of the reservoir from a secondportion of the reservoir with a first arcuate wall located within thereservoir; delivering the shear fluid from the reservoir to the workingchamber; and bringing the viscous clutch to rest in an idle condition,wherein portions of the shear fluid are retained in both the accumulatorand the first portion of the reservoir in the idle condition to reducedrain back from the reservoir to the working chamber.

The method of the preceding paragraph can optionally include,additionally and/or alternatively, any one or more of the followingfeatures, configurations and/or additional steps:

the shear fluid can pass from the accumulator to the reservoir in aradial direction at a single circumferential location.

A method for use with a viscous clutch can include pumping a shear fluidradially inward from a working chamber to an accumulator; passing theshear fluid from the accumulator to a reservoir having a closedconfiguration; moving all of the shear fluid from the accumulator alonga reservoir path having a tortuous shape that traverses an angular rangeof at least 540° relative to an axis of the clutch; delivering the shearfluid from the reservoir to the working chamber; and bringing theviscous clutch to rest in an idle condition, wherein portions of theshear fluid are retained in both the accumulator and an upstream portionof the reservoir path in the idle condition to reduce drain back fromthe reservoir to the working chamber.

The method of the preceding paragraph can optionally include,additionally and/or alternatively, any one or more of the followingfeatures, configurations and/or additional steps:

the shear fluid can pass from the accumulator to the reservoir in aradial direction at a single circumferential location.

A viscous clutch can include an input member; an output member; aworking chamber defined between the input member and the output member;a reservoir to hold a supply of a shear fluid, the reservoir fluidicallyconnected to the working chamber by a fluid circuit; an outlet to passthe shear fluid from the reservoir to the working chamber along thefluid circuit; a return bore to return the shear fluid pumped out of theworking chamber along the fluid circuit; a first wall having an arcuatesegment, the first wall positioned within the reservoir to separate afirst portion of the reservoir from a second portion of the reservoir;and a second wall having an arcuate segment, the second wall positionedwithin the reservoir radially adjacent to the first wall to separate athird portion of the reservoir from the first and second portions of thereservoir.

The viscous clutch of the preceding paragraph can optionally include,additionally and/or alternatively, any one or more of the followingfeatures, configurations and/or additional components:

the reservoir can have an inlet bore providing an inlet to the reservoiralong the fluid circuit, and wherein the inlet bore and the outlet boreare aligned at a common circumferential location.

A viscous clutch can include an input member; an output member; aworking chamber defined between the input member and the output member;a reservoir to hold a supply of a shear fluid, the reservoir fluidicallyconnected to the working chamber by a fluid circuit; an outlet to passthe shear fluid from the reservoir to the working chamber along thefluid circuit; a return bore to return the shear fluid pumped out of theworking chamber along the fluid circuit; and a first wall having anarcuate segment, a first end projection that radially connects thearcuate segment to a first circumferentially-extending boundary of thereservoir, and a second end projection that radially connects thearcuate segment to a second circumferentially-extending boundary of thereservoir, wherein the second end projection is located opposite thefirst end projection along the arcuate segment, and wherein the firstwall is positioned within the reservoir to separate a first portion ofthe reservoir from a second portion of the reservoir.

The viscous clutch of the preceding paragraph can optionally include,additionally and/or alternatively, any one or more of the followingfeatures, configurations and/or additional components:

the first circumferentially-extending boundary of the reservoir can bean outer boundary, and the second circumferentially-extending boundaryof the reservoir can be an inner boundary;

the arcuate segment of the first wall can extend about an angular rangeβ with respect to an axis of the viscous clutch, the angular range βbeing greater than or equal to 540°;

the first end projection can include a substantially planar portionjoined to the arcuate segment by a radiused corner that protrudesradially inward from the arcuate segment;

the first end projection can have a convex shape in a circumferentialdirection;

at least a portion of the arcuate segment of the first wall can have ahelical shape;

the arcuate segment of the first wall can have a circular portion at adownstream end proximate an outlet bore of the reservoir, and ahelically-shaped portion of the arcuate segment can be located upstreamof the circular portion;

the fluid circuit can include a reservoir path through the reservoir,and a cross-sectional area of the reservoir can vary along the reservoirpath; and/or

a cross-sectional area of the reservoir is larger at a middle portion ofa reservoir path through the reservoir than at both an upstream end anda downstream end of the reservoir path.

A viscous clutch can include an input member; an output member; aworking chamber defined between the input member and the output member;a reservoir to hold a supply of a shear fluid, the reservoir fluidicallyconnected to the working chamber by a fluid circuit; an outlet bore topass the shear fluid from the reservoir to the working chamber along thefluid circuit; a return bore to return the shear fluid pumped out of theworking chamber along the fluid circuit; a first wall having an arcuatesegment, wherein the first wall is positioned within the reservoir toseparate a first portion of the reservoir from a second portion of thereservoir; and a second wall having an arcuate segment, the second wallpositioned within the reservoir radially adjacent to the first wall toseparate a third portion of the reservoir from the first and secondportions of the reservoir.

The viscous clutch of the preceding paragraph can optionally include,additionally and/or alternatively, any one or more of the followingfeatures, configurations and/or additional components:

wherein the reservoir has an inlet bore providing an inlet to thereservoir along the fluid circuit, and wherein the inlet bore and theoutlet bore are aligned at a common circumferential location;

the first and second walls can each have a free end, and the free endscan be arranged on opposite sides of the common circumferentiallocation;

the arcuate segment of the first wall can extend about an angular rangeβ1 with respect to an axis of the viscous clutch, the angular range β1being greater than or equal to 330°, and the arcuate segment of thesecond wall can extend about an angular range β2 with respect to an axisof the viscous clutch, the angular range β2 being greater than or equalto 330°;

the first wall can further include a first end projection that radiallyconnects the arcuate segment of the first wall to a firstcircumferentially-extending boundary of the reservoir, and the secondwall can further include a second end projection that radially connectsthe arcuate segment of the second wall to a secondcircumferentially-extending boundary of the reservoir;

the first circumferentially-extending boundary of the reservoir can bean outer boundary, and the second circumferentially-extending boundaryof the reservoir can be an inner boundary;

the first wall can be positioned closer to the outer boundary than tothe second wall; and/or

the first end projection can include a substantially planar portionjoined to the arcuate segment by a radiused corner that protrudesradially inward from the arcuate segment.

A viscous clutch can include an input member; an output member; aworking chamber defined between the input member and the output member;a reservoir to hold a supply of a shear fluid, the reservoir fluidicallyconnected to the working chamber by a fluid circuit; an outlet to passthe shear fluid from the reservoir to the working chamber along thefluid circuit; a return bore to return the shear fluid pumped out of theworking chamber along the fluid circuit; and an accumulator positionedradially inward from the reservoir and separated from the reservoir by acommon circumferential wall, wherein a single bore passes radiallythrough the common circumferential wall to fluidically link theaccumulator and the reservoir.

The viscous clutch of the preceding paragraph can optionally include,additionally and/or alternatively, any one or more of the followingfeatures, configurations and/or additional components:

the accumulator and the reservoir can be axially aligned; and/or

the reservoir and the accumulator can both be carried by androtationally fixed to the input member so as to co-rotate at all timeswith the input member.

Summation

Any relative terms or terms of degree used herein, such as“substantially”, “essentially”, “generally”, “approximately” and thelike, should be interpreted in accordance with and subject to anyapplicable definitions or limits expressly stated herein. In allinstances, any relative terms or terms of degree used herein should beinterpreted to broadly encompass any relevant disclosed embodiments aswell as such ranges or variations as would be understood by a person ofordinary skill in the art in view of the entirety of the presentdisclosure, such as to encompass ordinary manufacturing tolerancevariations, incidental alignment variations, transient alignment orshape variations induced by thermal, rotational or vibrationaloperational conditions, and the like. Moreover, any relative terms orterms of degree used herein should be interpreted to encompass a rangethat expressly includes the designated quality, characteristic,parameter or value, without variation, as if no qualifying relative termor term of degree were utilized in the given disclosure or recitation.

Although the present invention has been described with reference topreferred embodiments, workers skilled in the art will recognize thatchanges may be made in form and detail without departing from the spiritand scope of the invention. For instance, features of one disclosedembodiment can be utilized with other disclosed embodiments.

1-31. (canceled)
 32. A viscous clutch comprising: an input member; anoutput member; a working chamber defined between the input member andthe output member; a reservoir to hold a supply of a shear fluid, thereservoir fluidically connected to the working chamber by a fluidcircuit; an outlet bore to pass the shear fluid from the reservoir tothe working chamber along the fluid circuit; a return bore to return theshear fluid pumped out of the working chamber along the fluid circuit; afirst wall having an arcuate segment, the first wall positioned withinthe reservoir to separate a first portion of the reservoir from a secondportion of the reservoir; and a second wall having an arcuate segment,the second wall positioned within the reservoir radially adjacent to thefirst wall to separate a third portion of the reservoir from the firstand second portions of the reservoir.
 33. The viscous clutch of claim32, wherein the reservoir has an inlet bore providing an inlet to thereservoir along the fluid circuit, and wherein the inlet bore and theoutlet bore are aligned at a common circumferential location.
 34. Aviscous clutch comprising: an input member; an output member; a workingchamber defined between the input member and the output member; areservoir to hold a supply of a shear fluid, the reservoir fluidicallyconnected to the working chamber by a fluid circuit; an outlet to passthe shear fluid from the reservoir to the working chamber along thefluid circuit; a return bore to return the shear fluid pumped out of theworking chamber along the fluid circuit; and a first wall having anarcuate segment, a first end projection that radially connects thearcuate segment to a first circumferentially-extending boundary of thereservoir, and a second end projection that radially connects thearcuate segment to a second circumferentially-extending boundary of thereservoir, wherein the second end projection is located opposite thefirst end projection along the arcuate segment, and wherein the firstwall is positioned within the reservoir to separate a first portion ofthe reservoir from a second portion of the reservoir.
 35. The viscousclutch of claim 34, wherein the first circumferentially-extendingboundary of the reservoir is an outer boundary, and wherein the secondcircumferentially-extending boundary of the reservoir is an innerboundary.
 36. The viscous clutch of claim 34, wherein the arcuatesegment of the first wall extends about an angular range β with respectto an axis of the viscous clutch, the angular range β being greater thanor equal to 540°.
 37. The viscous clutch of claim 34, wherein the firstend projection includes a substantially planar portion joined to thearcuate segment by a radiused corner that protrudes radially inward fromthe arcuate segment.
 38. The viscous clutch of claim 34, wherein thefirst end projection has a convex shape in a circumferential direction.39. The viscous clutch of claim 34, wherein at least a portion of thearcuate segment of the first wall has a helical shape.
 40. The viscousclutch of claim 39, wherein the arcuate segment of the first wall has acircular portion at a downstream end proximate an outlet bore of thereservoir, and wherein the helically-shaped portion of the arcuatesegment is located upstream of the circular portion.
 41. The viscousclutch of claim 34, wherein the fluid circuit includes a reservoir paththrough the reservoir, and wherein a cross-sectional area of thereservoir varies along the reservoir path.
 42. The viscous clutch ofclaim 41, wherein the cross-sectional area of the reservoir is larger ata middle portion of the reservoir path than at both an upstream end anda downstream end of the reservoir path.
 43. A viscous clutch comprising:an input member; an output member; a working chamber defined between theinput member and the output member; a reservoir to hold a supply of ashear fluid, the reservoir fluidically connected to the working chamberby a fluid circuit; an outlet bore to pass the shear fluid from thereservoir to the working chamber along the fluid circuit; a return boreto return the shear fluid pumped out of the working chamber along thefluid circuit; a first wall having an arcuate segment, wherein the firstwall is positioned within the reservoir to separate a first portion ofthe reservoir from a second portion of the reservoir; and a second wallhaving an arcuate segment, the second wall positioned within thereservoir radially adjacent to the first wall to separate a thirdportion of the reservoir from the first and second portions of thereservoir.
 44. The viscous clutch of claim 43, wherein the reservoir hasan inlet bore providing an inlet to the reservoir along the fluidcircuit, and wherein the inlet bore and the outlet bore are aligned at acommon circumferential location.
 45. The viscous clutch of claim 44,wherein the first and second walls each have a free end, the free endsarranged on opposite sides of the common circumferential location. 46.The viscous clutch of claim 44, wherein the arcuate segment of the firstwall extends about an angular range β₁ with respect to an axis of theviscous clutch, the angular range β₁ being greater than or equal to330°, and wherein the arcuate segment of the second wall extends aboutan angular range β₂ with respect to an axis of the viscous clutch, theangular range β₂ being greater than or equal to 330°.
 47. The viscousclutch of claim 43, wherein the first wall further comprises a first endprojection that radially connects the arcuate segment of the first wallto a first circumferentially-extending boundary of the reservoir, andwherein the second wall further comprises a second end projection thatradially connects the arcuate segment of the second wall to a secondcircumferentially-extending boundary of the reservoir.
 48. The viscousclutch of claim 47, wherein the first circumferentially-extendingboundary of the reservoir is an outer boundary, and wherein the secondcircumferentially-extending boundary of the reservoir is an innerboundary.
 49. The viscous clutch of claim 48, wherein the first wall ispositioned closer to the outer boundary than to the second wall.
 50. Theviscous clutch of claim 47, wherein the first end projection includes asubstantially planar portion joined to the arcuate segment by a radiusedcorner that protrudes radially inward from the arcuate segment. 51-53.(canceled)